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We have developed a technique for absolute measurements of electron density in pulse-repetitive microwave discharges in air. The technique is based on the time-resolved absolute intensity of a nitrogen spectral band belonging to the Second Positive System, the kinetic model and the detailed particle balance of the N2C3Πu (ν = 0) state. This new approach bridges the gap between two existing electron density measurement methods (Langmuir probe and Stark broadening). The electron density is obtained from the time-dependent rate equation for the population of N2C3Πu (ν = 0) using recorded waveforms of the absolute C3Πu → B3Πg (0-0) band intensity, the forward and reflected microwave power density. Measured electron density waveforms using numerical and approximated analytical methods are presented for the case of pulse repetitive planar surface microwave discharge at the aperture of a horn antenna covered with alumina ceramic plate. The discharge was generated in air at 11.8 Torr with a X-band microwave generator using 3.5 μs microwave pulses at peak power of 210 kW. In this case, we were able to time resolve the electron density within a single 3.5 μs pulse. We obtained (9.0 ± 0.6) × 1013 cm-3 for the peak and (5.0 ± 0.6) × 1013 cm-3 for the pulse-average electron density. The technique presents a convenient, non-intrusive diagnostic method for local, time-defined measurements of electron density in short duration discharges near atmospheric pressures. [ABSTRACT FROM AUTHOR]

Detailed characterization of a microwave cavity discharge in the supersonic flow of Ar/H2/Air mixtures at static pressures of 1–10 Torr and Mach number 2 is mostly based on emission spectroscopy techniques. In the conditions close to real combustion environments, effects of hydrogen and air admixture to plasma parameters and population of excited species in the discharge are demonstrated. The effects resulting in ionization loss are discussed from the aspects of dominant mechanisms and consequences for the plasma assisted hydrogen oxidation. [ABSTRACT FROM AUTHOR]

The air plasma effluent of an arc-seed microwave torch is used to kill bacterial spores contained inside an envelope. The torch is operated at a 60-Hz periodic mode (with about 40% duty cycle) and runs stably at a low airflow rate (e.g., 0.3931/s). The images of plasma torch plumes show that the arc loop of the discharge prolongs from the electrodes by nearly 3 cm and microwave energizes the charge particles along the arc loop considerably. The emission spectroscopy of the torch indicates that the plasma effluent contains an abundance of reactive atomic oxygen. Bacillus cereus is chosen for the biological agent in the decontamination experiment. The experiment and the decontamination efficacy of this torch are presented. The averaged temperature inside the envelope is measured to be less than 40 °C, thus ruling out the thermal decontamination mechanism. [ABSTRACT FROM AUTHOR]

The levitation of objects above a microwave horn is demonstrated. High-power microwave pulses generate a low-temperature, diffuse plasma on the surface of the horn window. The thermal effect of the surface plasma brings about a localized increase in the pressure and results in a vertical flow of air, thus levitating the object. [ABSTRACT FROM AUTHOR]

An innovative type of subcritical streamer discharge, generated by bursts of focused microwave (MW) radiation in transverse electromagnetic mode with wavelength of 10 cm, pulse duration of 40 µs, and intensity of 5.6 × 10[sub 4] W/cm², was initiated at the surface of a polymer foil at 420 Torr in air. The MW field of a quasioptical beam was three times lower than the critical breakdown field. Exposure of a polymer foil to the discharge caused a transition from hydrophobicity to hydrophilicity. [ABSTRACT FROM AUTHOR]